R51/3 No Spark

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johnstas617
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Joined: Sun Jul 12, 2015 4:46 pm

R51/3 No Spark

Post by johnstas617 »

R51/3
No spark
Engine after rebuild
Didn’t touch the electronics
S Mark at the window.
Magnetto and coil assembly aligned by
the “ | “ mark . Also the rotor with arrow pointed up.
What could be wrong ?

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schrader7032
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Re: R51/3 No Spark

Post by schrader7032 »

Points opening and closing? Is there a spark safety gap on the coil like there is on a /2? There's supposed to be a 10-11mm gap there. If the gap is too close, the spark will take the path of least resistance and jump across the safety gap and not at the plugs.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

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skyler.robbins
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Re: R51/3 No Spark

Post by skyler.robbins »

Did something accidently get disconnected in the headlight bucket?..
Is the key getting a full connection?

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johnstas617
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Re: R51/3 No Spark

Post by johnstas617 »

skyler.robbins wrote:
Sat Aug 01, 2020 12:12 am
Did something accidently get disconnected in the headlight bucket?..
Is the key getting a full connection?
Yes all good up there .

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johnstas617
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Re: R51/3 No Spark

Post by johnstas617 »

schrader7032 wrote:
Fri Jul 31, 2020 4:11 pm
Points opening and closing? Is there a spark safety gap on the coil like there is on a /2? There's supposed to be a 10-11mm gap there. If the gap is too close, the spark will take the path of least resistance and jump across the safety gap and not at the plugs.
Yes they open and close, but I will measure the gap.
At what position of the flywheel the gap should be at its widest point?

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schrader7032
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Re: R51/3 No Spark

Post by schrader7032 »

johnstas617 wrote:
Sat Aug 01, 2020 5:24 am
At what position of the flywheel the gap should be at its widest point?
Not at the S-mark! To tell the truth, I don't know that I've ever seen anyone mention a position. I think you just have to watch the gap as you rotate the engine. If you don't see the gap open, then they need to be adjusted.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

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johnstas617
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Re: R51/3 No Spark

Post by johnstas617 »

Replaced points
Adjusted the gap to 0.4 mm
Still no spark

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schrader7032
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Re: R51/3 No Spark

Post by schrader7032 »

Have you measure the resistance of the coil? What are the ohms measured from one spark plug cap to the other cap?
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

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johnstas617
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Re: R51/3 No Spark

Post by johnstas617 »

12.2Kohm

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schrader7032
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Re: R51/3 No Spark

Post by schrader7032 »

Well, that's not a bad number one way or the other. Some limited notes I have suggest maybe 15-17K might be expected, but you're in the ballpark.

Assembly of the magneto back on the bike is important. I wonder if there's an insulating washer that is in the wrong spot and things are being grounded or not grounded. I would recheck all that...if you have notes or pictures from before, maybe that will help.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

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